Showing papers on "Particle horizon published in 1987"
TL;DR: A cosmological model with an additional term Λ(x)gμν in the energy-momentum tensor is introduced in this article, and the model displays a flow of energy from curvature to matter such that the entropy of matter is not conserved.
299 citations
TL;DR: In this paper, a review of recent results concerning the global structure of the inflationary universe, which have been obtained within stochastic approach to inflation, is given, and it is shown in particular that the evolution of the universe in the chaotic inflation scenario has no end and may have no beginning.
Abstract: In this article we give a review of recent results concerning the global structure of the inflationary universe, which have been obtained within stochastic approach to inflation. It is shown in particular that the evolution of the universe in the chaotic inflation scenario has no end and may have no beginning. In this scenario the major part of the physical volume of the universe always remains in the inflationary phase. During inflation the universe becomes divided into many exponentially large domains, inside which all possible metastable vacuum states and all possible types of compactification compatible with inflation are realized.
220 citations
TL;DR: In this article, the detailed construction of six Regge spacetimes, each being an approximation to a time symmetric Friedmann dust-filled universe, is presented, and the evolution of the Regge spaces is seen to terminate prior to the full collapse of the universe.
Abstract: The detailed construction of six Regge spacetimes, each being an approximation to a time symmetric Friedmann dust-filled Universe, are presented. These spacetimes are a generalisation of those originally constructed by Collins and Williams (1973). This paper presents new methods for the subdivision of each Cauchy surface into a set of tetrahedra, for the construction of the general four-dimensional block and for the implementation of the constraints of homogeneity and isotropy. A new action sum for pure dust in a Regge spacetime is also presented. The evolution of the Regge spaces is seen to terminate prior to the full collapse of the Universe. This is shown to occur when the particle horizon for an observer at the centre of one tetrahedron has contracted so as to just touch the vertices of that tetrahedron. It is argued that this is a generic feature and will occur in any Regge spacetime whenever the local curvature becomes too large.
33 citations
TL;DR: In this paper, the kinematics of such models, where the smooth component is relativistic particles, a cosmological term, a network of light strings, or fast-moving, light strings is studied in detail.
Abstract: Theoretical prejudice and inflationary models of the very early universe strongly favor the flat, Einstein-de Sitter model of the universe. At present the observational data conflict with this prejudice. This conflict can be resolved by considering flat models of the universe which posses a smooth component of energy density. The kinematics of such models, where the smooth component is relativistic particles, a cosmological term, a network of light strings, or fast-moving, light strings is studied in detail. The observational tests which can be used to discriminate between these models are also discussed. These tests include the magnitude-redshift, lookback time-redshift, angular size-redshift, and comoving volume-redshift diagrams and the growth of density fluctuations.
28 citations
TL;DR: In this article, a cosmological model based on interpretation of the red shift by decrease of the light speed with time everywhere in the Universe beginning with a certain moment of time in the past is discussed.
Abstract: A cosmological model is discussed which is based on interpretation of the red shift by decrease of the light speed with time everywhere in the Universe beginning with a certain moment of time in the past. The model is described by a metric in which the light speed depends on time and the radius of the curvature of three-dimensional space remains constant (c-metric). It is shown that this metric leads to the same observed facts and formulas of different characteristics that the metric of standard cosmology does but with essentially different physical interpretation. Such a property is the consequence of conformity of spaces being defined by both metrics. The agreement with the fundamental physics laws is achieved by introducing the evolution of a number of other fundamental constants synchronously with the variation of the light speed. The model considered connected the evolution of the Universe with evolution of physical constants and permits explaining some unclear cosmological phenomena — for example, a high isotropy of the relict background and superluminal speed in quasars.
19 citations
TL;DR: In this article, the wave function of the universe is interpreted as giving the probability for the universe to appear from nothing, which is not a correct interpretation since the normalization presupposes a universe, not nothing.
Abstract: Hawking and Hartle interpreted their wave function of the universe as giving the probability for the universe to appear from nothing. However, this is not a correct interpretation, since the normalization presupposes a universe, not nothing. Transition probabilities require a measure on the initial state and a physical result requires a physical initial state.
9 citations
TL;DR: In this article, a new solution of Einstein's field equations is found, which describes a dust-filled Kantowski-Sachs universe with a positive cosmological constant, where the mass density of the dust is positive.
8 citations
TL;DR: The Hartle-Hawking wave function of a homogeneous-isotropic rotating universe has been found in this article and it is shown that the universe with large global rotation is unlikely.
8 citations
TL;DR: In this article, the authors show that the part of the universe that is observable today (in principle) could not have evolved out of a domain which was causally connected in the past.
Abstract: We show that, the part of the universe that is observable today (in principle), could not have evolved out of a domain which was causally connected in the past. This and other issues related to horizon problem in inflationary models are discussed.
6 citations
TL;DR: It has been shown that if the size of the universe with topologically compactified manifold is smaller than the present horizon, then the multiply connected topology with global anisotropy can not be ruled out by the observed isotropy of microwave background radiation as mentioned in this paper.
Abstract: It has been shown that if the size of the universe with topologically compactified manifold is smaller than the present horizon, then the multiply connected topology with global anisotropy can not be ruled out by the observed isotropy of microwave background radiation.
5 citations
01 Jan 1987
TL;DR: Hartle as discussed by the authors reviewed and outlined the basic physical nature of these two mechanisms, leaving out the details, and referred the reader to more comprehensive reviews and to the primary literature throughout these lectures.
Abstract: The observed universe is homogeneous and isotropic on the largest observable scales. The best evidence for this comes from observations of the cosmic background radiation (CBR). On smaller scales, a striking amount of structure can be seen — galaxies, clusters of galaxies, and the “large scale structure” in the form of possible filaments, bubbles, sheets or voids. The best proximate explanation for this structure is small amplitude perturbations in the early universe, which grew by gravitational instability into the observed large scale structure during the expansion of the universe. At some time in the future when we have a complete theory of the universe and its initial conditions — see James Hartle’s lectures in this volume1 for some promising ideas toward such a theory — both the overall homogeneity and the structure should be a calculable consequence of the theory. Until then, people have made partial progress toward understanding the genesis of structure on a homogeneous background, based on the laws of fundamental physics as currently known. At this time we have at least two possible fundamental mechanisms for generation of the conjectural initial perturbations, namely quantum fluctuations, or thermodynamic fluctuations of a particular sort. My purpose in these lectures is to review and outline the basic physical nature of these two mechanisms, leaving out the details. Both mechanisms are well reviewed in the literature, and the reader will be referred both to more comprehensive reviews and to the primary literature throughout these lectures.
TL;DR: In this article, exact solutions for radiation-filled cosmological differential equations of Brans-Dicke theory with the assumption that the radius of curvatureQ of the universe varies directly as thenth power of time were obtained.
Abstract: Considering a Robertson-Walker line element, exact solutions are obtained for radiation-filled cosmological differential equations of Brans-Dicke theory with the assumption that the radius of curvatureQ of the universe varies directly as thenth power of time. The solution is found to be valid for closed space only and the coupling constantw of the scalar tensor theory is necessarily negative. The radius of curvature of increases linearly with respect to the age of the universe, while the gravitational constantk varies directly as the square of the radius of the universe. The solution obtained is in contradiction to Dirac's hypothesis, in which the gravitational constant should decrease with time in an expanding universe.
TL;DR: In this paper, it was shown that the universe departed from the thermal equilibrium in the past by an interplay among dynamic instability, matter differentiation and weakening of some interactions, and that this was the outcome of an interaction between dynamic instability and matter differentiation.
Abstract: The relic microwave radiation indicates that the universe was in the state of thermal equilibrium (heat death) in the past. The question arises how could it happen that the universe departed from the thermal equilibrium? According to the models presented here this was the outcome of an interplay among dynamic instability, matter differentiation and weakening of some interactions.
TL;DR: In this paper, the Stanyukovich formula S ∼ N3/2 is derived for the rotation of the observable universe, which is based on the existence of Eddington-Dirac large numbers.
Abstract: We study the problem of a possible rotation of the observable Universe (Metagalaxy) from the point of view of the general-relativistic theory of gravitation. We employ the concept of a hierarchical structure of reality, based on the existence of Eddington-Dirac “large numbers.” From the Einstein equations in their Landau-Raichaudhuri form we derive expressions for the angular momentum and angular velocity ω of the rotation of the Metagalaxy. These expressions give an ω coinciding in order of magnitude with the observed one. Using the formulas obtained, and using the hierarchy relation (“large number” relation), we obtain the Stanyukovich formula S ∼ N3/2 which relates the number of nucleons in the Metagalaxy N and its angular momentum S. We show that the angular velocity may decrease in inverse proportionality to the scale factor, which may explain its small value at this time. We show that the source of rotation in cosmology can be space-time torsion, induced by the spin of fermionic matter.
TL;DR: In this paper, it was shown that, in order for plane accumulations of matter with a density much greater than the mean density of the matter in the Universe to exist in the universe at the present time, perturbations of the density are necessary at the time of recombination.
Abstract: The general solution of Einstein's equations with the energy-momentum tensor of an ideal dust in the plane-symmetric case is used to obtain the generalization of the solutions for scalar perturbations in a spatial-plane Friedman universe. It is shown that, in order for plane accumulations of matter with a density much greater than the mean density of the matter in the Universe to exist in the Universe at the present time, perturbations of the density are necessary at the time of recombination, (δɛ/ɛ)p ∿ 10−4.
TL;DR: In this paper, the issue of whether the present observational evidence that the mean mass density of the universe is less than the critical density (i.e., μ < 1) implies an infinite future expansion of the observable universe is discussed.
Abstract: The issue of whether the present observational evidence that the mean mass density of the universe is less than the critical density (i.e., μ<1) implies an infinite future expansion of the universe is discussed. Although in conventional cosmological scenarios μ<1 necessarily leads to a universe that will grow infinitely old, this conclusion can be avoided in ways which are reasonably natural. One of these is to assume the existence of a small negative cosmological constant. Another way is to postulate the existence of unstable fields with a long time scale for the onset of the instability. An example is a scalar field with a negative squared mass and ¦m¦≲10−32eV. Other examples include fields for which the instability is generated by quantum corrections in curved space-time. All of these are capable of halting the expansion of an open universe and forcing it to recollapse into a “big crunch.”
TL;DR: In this paper, a model for continuously following a model of a universe that in its evolution makes a transition from one type of universe to another is presented, where the epoch when the universe changes from being radiation-dominated to being matter-dominated is related to the epoch of radiation decoupling from matter.
Abstract: A method is given for continuously following a model of a universe that in its evolution makes a transition from one type of universe to another. As an illustration, a universe is considered that initially is radiation-dominated and then makes a transition to a final matter-dominated Einstein-de Sitter universe. The epoch when the universe changes from being radiation-dominated to being matter-dominated is found and is related to the epoch when radiation decouples from matter.
TL;DR: In this article, the authors argue that the density of the universe is not the minimum required to prevent indefinite expansion, but the evidence is not all on their side, and they point out that the existence of infinite numbers of stars is not a sign of infinite expansion.
Abstract: Astronomers hanker after the notion that the density of the Universe is the minimum required to prevent indefinite expansion, but the evidence is not all on their side.
TL;DR: In this paper, the exterior field of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant was considered and it was shown that the exterior solution of this universe is simply the empty space-time of general relativity.
Abstract: The exterior field of the Robertson-Walker metric in the Lyttleton-Bondi universe with cosmological constant is considered. It is shown that in the presence of cosmological constant, the exterior solution of this Universe is simply the empty space-time of general relativity.
TL;DR: In this article, the cosmological constant A and the density parameter f.1 depend on the decay time and the cosmic ages are found to be of the order of or larger than 0.6/Ho in the fitted models.
Abstract: Decaying-particle universe models with nonzero cosmological constant A are considered in connection with the recent observational [Galaxy number count N-redshift zl relation and it is shown that the best-fitted values of A and the density parameter f.1 depend on the decay time td: For Hotd =0.05, we get .G,=0.494 and Ac2/(3Ho2) = -0.046. If the model is required to be fiat, the fitted values are f.1=0.689 and Ac2/(3Ho2)=0.311 for Hotd=0.05. The cosmic ages are found to be of the order of or larger than 0.6/Ho in the fitted models. Moreover the nonlinear growth of the density perturbations is considered and the evolution of the baryon density is examined in several fitted models.